so does a p0128 turn on CEL or do you have to scan for it?

 

Your numbers seem very much normal.

 

Mine seems to do that too. Although I'm not sure that if' after I turned the a/c off and drove it for several more miles on a cool day, that the fan would still running.

I have an HHR 2.2 that runs a little over 180, and an SS that runs 189 to 190. Both occasionally a bit higher, never a lot higher. Could be slight variation in ether the thermostat or sensor, or both. I'm not messing with them. I understand the SS fan control is a little more complicated, which makes sense, because turbo. Never needed to get into it.

 

I see nothing wrong with those Temps. Water boils at 212, that's in an open system. Figure in the pressure cap, boiling point goes up. Figure in the coolant, boiling point goes up more.

The thermostat's job is to keep the coolant above 180. Your thermostat is doing it's job.

 

The P0128 turns on the CEL

 

P0128 is when the temp is too LOW or does not get to 180F quick enough.
T-stats don't cause overheating.
The others don't work because the inner rubber gasket detaches from the valve and gets wedged into the valve opening causing it to stay open. And they are not as precise, the wax in them melts at an unpredictable rate.

That brass capsule is full of wax. When it melts the valve opens because wax expands when hot. Then when the temp goes back below the melt temp the valve closes.

The fan and radiator cool the water. The fan on a LT/LS turns on at about 219F and turns off when the temp gets back to 180F The SS has a variacle speed fan controlled by PWM.

 

I just said the thermostat in question will fail eventually and P0128 will show eventually.
The higher heat is most likely trapped air or faulty water pump or broken balance shaft chain… there other factors

 

well….got no weird noises….no codes as of yet….thinking air cause got more coolant in it late yesterday and acting more reasonable today….gonna keep checking for burping….